If the gear designer closely follows ISO-1302, all roughness parameters, limits, and the proper profilometer setup will be specified within the Check Mark Diagram.

The following briefly reviews the evolution of the diagram. The basic symbol indicating that a surface texture requirement exists is a check mark graphic as shown in Figure 2.

Figure 2: Basic graphic

The complete graphical symbol that is used to specify a roughness parameter, limit, and measurement parameters will include a horizontal line extending from the longer arm of the check mark graphic as shown in Figure 3.

Figure 3: Complete graphic

To indicate whether material is or is not to be removed from the surface to achieve the specified roughness parameter, a bar or circle is added to the check mark as shown in Figure 4a and Figure 4b.

Figure 4a: The bar indicates material is to be removed

Figure 4b: The circle indicates material is not to be removed

Roughness, Limits, and Profilometer Setup

To eliminate the possibility of uncertainty, all of the surface roughness parameters, limits, and profilometer setup parameters needed to complete the roughness specification must be placed in and around the Check Mark Diagram as shown in Figure 5

(a) This location is for the surface roughness parameter, the roughness numerical limits, and the profilometer filter and sample length.

(b) This location is any secondary roughness parameter as found in (a); a third surface roughness parameter would be located below (b).

(c) This location is for the method of manufacturing of the designated surface (i.e., turned, ground, or isotropic superfinished).

(d) This location is the orientation of the lay, relative to the plane of the drawing.

(e) This location is for the required machining allowance, if any.

Check Mark Diagram for Precision Gears

Following the format of Figure 5, a complete Check Mark Diagram for a precision ground gear with roughness limits of Ra < 0.4 µm and Rz < 2.4 µm can be found in Figure 6 with explanations shown in Table 1. Note that the orientation of the grinding on the tooth is parallel to the axis of the gear and the Ra/Rz values are displayed in µin.

Similarly, a complete Check Mark Diagram for an isotropically superfinished gear can be found in Figure 7. As mentioned in the January column, Ra, Rz, and Rmr are the recommended minimum roughness parameters to be used when specifying a gear surface (note that Rmr is missing from this Check Mark Diagram).

Additional Required Roughness Information

Any additional surface finish information not included in the Check Mark Diagram, but required to make the specification unambiguous — such as the number of measurements, location of measurements, or alternative stylus tip size — should be placed in a text box section of the gear drawing. The text box reference should be placed adjacent to the Check Mark Diagram for consistency (see Figure 6). Examples of additional information for insertion in a gear drawing text box can be, but not limited to, the following:

Conclusion

By following ISO-1302 (2002), a complete roughness specification can be designated with the Check Mark Diagram. As noted in the December Materials Matter column, “Gear Surfaces and Operational Performance,” the surface of a gear has a profound impact on its performance. With this in mind, the importance of the correct use of a complete Check Mark Diagram to eliminate the ambiguity of surface roughness limits on teeth flanks is clearly seen.